Problem passing formulas to an expression in a pivot table

[#1]

I'm having a problem passing formulas to an expression in a pivot table. The project I'm working on is confidential and I'm not allowed to show any part of it, so I've created a very simple example... Please bear with me.

In my script, I define this...

SET f_Something = '$1';

If I use the following as the expression in a pivot table

     $(f_Something('HI'))

then it works and I get     HI

There are several formulas that I will possible need to use in the expression, so I've loaded them from a table. I can already correctly select the correct formula to replace in the expression, but when I do this, it doesn't work (I get null).

For example, suppose F will contain the formula I'd like to replace and it currently equals f_Something('HI')

then if I use the following as the expression:

     =F

I'll see f_Something('HI'), which is exactly what I'd expect to see.

Now, I want to execute that function. I've tried:

$(F)

$(=F)

=$(F)

But all return null. How do I get the dollar expansion to execute my function and give me the correct result, which is

HI

Thanks!